Error the dropdown list in gridview when call the edit template

protected void gridFeesType_RowEditing(object sender, GridViewEditEventArgs e)
    {
        DataTable dts1 = (DataTable)ViewState["Data"];
        gridFeesType.EditIndex = e.NewEditIndex;
        int RowIndex = e.NewEditIndex;
        ViewState["row"] = RowIndex;
        
      DropDownList ddl = (DropDownList)gridFeesType.Rows[RowIndex].FindControl("TermofFees") as DropDownList;
     
        Table_();
        DataTable dtedit = (DataTable)ViewState["Table"];

ERROR--> object reference not set to instance object..

        ddl.SelectedItem.Text = dtedit.Rows[RowIndex]["TermofFees"].ToString();
    }